A study published Tuesday cast doubt on speculation that biological or genetic differences cause cancers to spread more aggressively in blacks than whites, leading to lower cancer survival rates.

More likely, the report from Memorial Sloan-Kettering Cancer Center in New York concluded, the well-documented disparity in survival rates between the races is caused by other factors including co-existing medical conditions.

In the United States, 63 percent of white cancer patients survive after five years -- compared to 52 percent of blacks. Income, insurance coverage, general health and time of diagnosis are all thought to play a part in that disparity.

Blacks suffer disproportionately from such problems as diabetes and heart disease, studies have shown.

The findings published Tuesday were based on a review of all English language studies comparing survival for black and white cancer patients published from 1996 to January 2002. It covered 189,877 white and 32,004 black patients.

The researchers found that in cases where black and white cancer patients received equal treatment -- comparable care at a similar stage of the disease -- blacks still had a slight survival disadvantage. But once deaths from all other health conditions were considered, cancer survival was basically the same, the report said.

"There is not much evidence that cancer behaves differently in blacks than in whites. Differences in treatment, stage of disease at presentation and mortality from other diseases -- not biological or genetic differences -- seem to explain most of the disparity," said Colin Begg, chairman of the Department of Epidemiology and Biostatistics at Memorial Sloan-Kettering.

"These are the areas that should be the primary targets for future research and public health interventions," he added.

The study was published in this week's Journal of the American Medical Association.

The study did find that blacks were at a significantly higher risk of death from three types of cancer -- breast cancer and two relatively rare cancers, uterine and bladder. There was no appreciable difference in death rates from lung, colorectal, prostate and eight other cancers assessed in the study.

"These findings suggest that if biological differences do exist, they are responsible for at most a very small fraction of all cancer deaths," the report concluded. "Therefore, biological differences between blacks and whites cannot explain a meaningful share of the racial disparity in cancer survival observed in the United States," it added.